This invention relates to the heat exchanger art and, more particularly, to a compact air-to-air heat exchanger, adapted for use with and in a gas turbine engine of the fan bypass type having a hot flow of cooling air, a cool flow of fan air, and a primary fan air stream duct in which a first portion of the cool flow of fan air flows.
It is well known in the art that, as the gas turbine engine combustor exit temperatures are increased toward stoichiometric, a larger percentage of engine air is required to cool the hot turbine and its parts. It is equally well known in the art that, as higher Mach numbers are attained, and as larger compressor ratios are achieved, with gas turbine engines, the temperature of the compressor discharge air (hereinafter referred to herein, as it is in the art, as the "cooling air" of the engine) is driven to well above 1000 degrees Fahrenheit. Since this cooling air is used to cool the high pressure turbine and its parts, the high temperature of the cooling air also tends to increase the percentage of engine air that is required to cool the turbine and its parts. Therefore, there exists in the art the problem of reducing the total percentage of cooling air that is required to cool the turbine, and the parts thereof, of the gas turbine engine.
Additionally, if a fuel-to-air heat exchanger is used in a gas turbine engine, fire prevention is another inherent problem, because if fuel leaks into the cooling air (which is at high pressure and at high temperature), a fire is almost assured.
I have eliminated, or at least have minimized, these two problems (i.e., the need for an increased total percentage of cooling air to cool the turbine and its parts; and, the need to prevent a fire) by devising a structurally compact and novel air-to-air heat exchanger which I dispose uniquely internal of the gas turbine engine, with my heat exchanger not only being literally and absolutely "fire safe", but also permitting, by its use in the engine, a lesser total percentage of cooling air (than is presently needed) to cool the hot turbine and its parts.
I have, therefore, significantly advanced the state-of-the-art.